How you would use rhino3dm inside rhino (i know it is not the reason it was created for), you would still need to convert python types to rhinocommon ones?
Don’t do this. The python bindings are built against public opennurbs and not the one that ships with Rhino. It will lead to eventual problems due to slight differences in the libraries.
We hope to some day build direct python bindings against the classes in Rhino, but that does not exist.